Bicycle sprocket and multiple bicycle sprocket assembly

ABSTRACT

A bicycle sprocket has a sprocket main body, a plurality of teeth disposed on the sprocket main body, and at least one shifting area. The teeth include at least one first tooth having a first maximum axial width and at least one second tooth having a second maximum axial width. The first maximum axial width is larger than the second maximum axial width. The first tooth is configured to engage with an outer link plate of a chain. The second tooth is configured to engage with an inner link plate of the chain. The at least one shifting area includes an area where a chain engages with one of the teeth during shifting from a small sprocket to the bicycle sprocket and an area where the chain separates from one of the teeth during a shifting action from the bicycle sprocket to the small sprocket.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/824,568, filed on May 17, 2013. Also, this application is acontinuation application of U.S. patent application Ser. No. 14/053,630,filed on Oct. 15, 2013. The entire disclosure of U.S. ProvisionalApplication No. 61/824,568 and U.S. patent application Ser. No.14/053,630 is hereby incorporated herein by reference.

BACKGROUND

Field of the Invention

This invention generally relates to a bicycle sprocket and a multiplebicycle sprocket assembly including the bicycle sprocket.

Background Information

Bicycle sprockets are provided both to a crank assembly located in themiddle of a bicycle and to the rear wheel, and the rotation of the crankassembly is transmitted to the rear wheel by a chain meshed with thesprockets. In a bicycle chain, an inner link plate and an outer linkplate are linked alternately; therefore, when the teeth of the sprocketshave the same thickness, the gaps between the outer link plate and theteeth of the sprockets are larger than the gaps between the inner linkplate and the teeth of the sprockets. In view of this, there areconventionally known sprockets (Specification of U.S. Pat. No.4,174,642, for example) in which the axial width of the teeth (the teeththickness), relative to the rotational center axis direction of thesprocket, is designed such that the axial width of the teeth meshingwith the outer link plate is larger than the axial width of the teethmeshing with the inner link plate. A conventional sprocket has teeththat taper diametrally outward. It is thereby unlikely that the gapsbetween the sprocket and chain will become smaller and that the chainwill separate from the teeth of the sprocket.

A multiple bicycle sprocket assembly comprises a plurality of sprockets.Among such multiple bicycle sprocket assemblies, one known example is abicycle crank assembly in which a plurality of sprockets havingdifferent numbers of teeth are mounted to a crank arm. The sprockets areprovided for shifting, and the chain is moved by a derailleur betweenthe two or more sprockets having different numbers of teeth to performthe shifting action.

SUMMARY

A sprocket having teeth that have different axial widths relative to therotational center axis direction of the sprocket is a structure forpreventing the chain from easily separating from the teeth of thesprocket. Therefore, when a sprocket having teeth that have differentaxial widths is employed in a conventional crank assembly for moving achain between two sprockets, the shifting action becomes complicated.

A problem of the present invention is to make the shifting action easierin a sprocket having teeth that have different axial widths.

A bicycle sprocket according to the present invention has a rotationalcenter axis and is capable of engaging with a chain. The bicyclesprocket comprises a sprocket main body, a plurality of teeth disposedalong a circumferential direction on the radially outer side of thesprocket main body, and at least one shifting area. The at least oneshifting area includes an area where the chain engages with one of theplurality of teeth of the bicycle sprocket during a shifting action froma small sprocket to the bicycle sprocket and an area where the chainseparates from one of the plurality of teeth of the bicycle sprocketduring a shifting action from the bicycle sprocket to the smallsprocket. The plurality of teeth include at least one tooth having afirst maximum axial width and at least one second tooth having a secondmaximum axial width, the first maximum axial width being larger than thesecond maximum axial width. The first tooth is formed to be capable ofengaging with an outer link plate of the chain. The second tooth isformed to be capable of engaging with an inner link plate of the chain.

In this bicycle sprocket, the chain is mounted to the sprocket so thatthe first tooth of greater axial width engages with an outer link, andthe second tooth of less axial width than the first tooth engages withan inner link. When the chain is disposed in at least one shifting areafor guiding the chain so that the chain readily separates from thesprocket teeth in order to shift, the chain is guided and moved toanother sprocket. Because at least one shifting area is provided to thesprocket, the shifting action is performed easily in the sprocket havingteeth that have different axial widths.

The plurality of teeth may include a plurality of first teeth. In thiscase, the bicycle sprocket can effectively hold the outer link of thechain.

The plurality of teeth may include a plurality of second teeth. In thiscase, the bicycle sprocket can effectively hold the inner link. Theplurality of teeth may include a plurality of first teeth and aplurality of second teeth. In this case, the bicycle sprocket caneffectively hold the outer link and the inner link of the chain.

At least some of the plurality of first teeth and the plurality ofsecond teeth may be disposed alternately in the circumferentialdirection. In this case, the chain can be more effectively preventedfrom easily separating from the teeth of the sprocket.

The first teeth may be formed into a + shape as seen from the radiallyouter side. In this case, because only part of the axial width isincreased rather than all of the axial width being increased, the weightof the sprocket can be prevented from increasing more than is necessaryeven if the axial width is increased.

The first teeth may be formed into a T shape as seen from the radiallyouter side. In this case, because only part of the axial width isincreased rather than all of the axial width being increased, the weightof the sprocket can be prevented from increasing more than is necessaryeven if the axial width is increased.

The first maximum axial width of the first teeth may be in a range of2.5 mm or greater and 5.4 mm or less. In this case, the first teeth canbe made to engage with the outer link instead of the inner link.

The first maximum axial width of the first teeth may be in a range of3.0 mm or greater and 4.5 mm or less. In this case, the first teeth canbe made to reliably engage with the outer link even if the chain is fora multi-speed rear sprocket assembly of ten or more speeds.

The second maximum axial width of the second teeth may be in a range of1.5 mm or greater and 2.3 mm or less. In this case, the second teeth canbe made to reliably engage with the inner link.

The shifting area may include shifting teeth provided to at least one ofany of the plurality of teeth. Because the shifting area includesshifting teeth formed into either a shape that allows the chain toseparate readily from the sprocket teeth or a shape that allows thechain to readily engage with the teeth of the other sprocket when thechain moves to the other sprocket, the shifting action can be performedsmoothly.

The shifting teeth may have guide surfaces for guiding the chain. Inthis case, a smooth shifting action is made possible because the chainis guided by the guide surfaces of the shifting teeth.

The shifting area may include at least one protuberance formed to becapable of supporting the chain. In this case, when the chain is guidedfrom the smaller-diameter sprocket to the larger-diameter sprocket, thechain can be supported on the larger-diameter sprocket by theprotuberance, and the chain therefore moves readily to thelarger-diameter sprocket.

At least one protuberance may include a first protuberance and a secondprotuberance formed to be capable of supporting the chain. In this case,due to the first protuberance and the second protuberance being disposedin different positions in the radial direction of the sprocket, thechain can be supported on the first protuberance and guided to thesecond protuberance, and the chain can be supported on the secondprotuberance and guided to the teeth of the sprocket. Therefore, thechain moves readily to the larger-diameter sprocket.

The distance between the first protuberance and the second protuberancemay be longer than the longitudinal length of an outer link of the chainand/or an inner link of the chain. In this case, the chain can besupported in a wide range by supporting different links of the chain onthe first protuberance and the second protuberance.

The distance between the first protuberance and the second protuberancemay be either equal to or shorter than the longitudinal length of anouter link of the chain and/or an inner link of the chain. The chain canbe reliably supported by supporting one link of the chain on the firstprotuberance and the second protuberance.

The shifting area may include a concave part disposed farther inward inthe radial direction than the base portions of the plurality of teeth.In this case, the chain can be efficiently guided to the larger-diametersprocket because the chain can be guided by the concave part fartherinward in the radial direction than the base portions.

A plurality of shifting areas may be provided. In this case, theshifting action can be performed quickly due to a plurality of shiftingareas being provided at intervals in the circumferential direction, forexample.

At least a pair of the shifting areas may be provided. In this case, dueto at least a pair of the plurality of shifting areas being provided atintervals in the circumferential direction, for example, the shiftingaction can be completed in one shifting area even if the shifting actionis not completed in another shifting area.

The bicycle sprocket according to the present invention may be a frontsprocket. In this case, it is possible to provide a front sprocketwhereby the chain can be stably held during the normal pedaling actionand a shifting action is also possible.

A bicycle sprocket according to another aspect of the present inventionhas a rotational center axis and is capable of engaging with a chain.The bicycle sprocket comprises a sprocket main body, a plurality ofteeth disposed along a circumferential direction on the radially outerside of the sprocket main body, and at least one shifting area. Theplurality of teeth include at least one first tooth having a firstmaximum axial width for engaging with an outer link plate of the chainand at least one second tooth having a second maximum axial width forengaging with an inner link plate of the chain. The first maximum axialwidth is larger than the second maximum axial width. The at least onefirst tooth includes a shifting tooth that is included in the at leastone shifting area. The shifting tooth is formed into a T shape as seenfrom the radially outer side.

In this bicycle sprocket, the chain is mounted to the sprocket so thatthe first tooth of greater axial width engages with an outer link, andthe second tooth of less axial width than the first tooth engages withan inner link. When the chain is disposed in at least one shifting areafor guiding the chain so that the chain readily separates from thesprocket teeth in order to shift, the chain is guided and moved toanother sprocket. Because at least one shifting area is provided to thesprocket, the shifting action is performed easily in the sprocket havingteeth that have different axial widths. Additionally, with this aspectof the invention, because only part of the axial width of the shiftingtooth is increased rather than all of the axial width being increased,the weight of the sprocket can be prevented from increasing more than isnecessary even if the axial width is increased.

A bicycle sprocket according to another aspect of the present inventionhas a rotational center axis and is capable of engaging with a chain.The bicycle sprocket comprises a sprocket main body, a plurality ofteeth disposed along a circumferential direction on the radially outerside of the sprocket main body, and at least one shifting area. Theplurality of teeth include at least one first tooth having a firstmaximum axial width for engaging with an outer link plate of the chainand at least one second tooth having a second maximum axial width forengaging with an inner link plate of the chain. The first maximum axialwidth is larger than the second maximum axial width. The first maximumaxial width is larger than the second maximum axial width, and the firstmaximum axial width of the first teeth is equal to or larger than 2.5 mmand smaller than or equal to 5.4 mm.

In this bicycle sprocket, the chain is mounted to the sprocket so thatthe first tooth of greater axial width engages with an outer link, andthe second tooth of less axial width than the first tooth engages withan inner link. When the chain is disposed in at least one shifting areafor guiding the chain so that the chain readily separates from thesprocket teeth in order to shift, the chain is guided and moved toanother sprocket. Because at least one shifting area is provided to thesprocket, the shifting action is performed easily in the sprocket havingteeth that have different axial widths. Additionally, due to the sizelimitation of the first maximum axial width, the first teeth can be madeto engage with the outer link instead of the inner link.

In this aspect of the invention, the first maximum axial width of thefirst teeth may be equal to or larger than 3.0 mm and smaller than orequal to 4.5 mm. In this case, the first teeth can be made to reliablyengage with the outer link even if the chain is for a multi-speed rearsprocket assembly of ten or more speeds.

In this aspect of the invention, the second maximum axial width of thesecond teeth may be equal to or larger than 1.5 mm and smaller than orequal to 2.3 mm. In this case, the second teeth can be made to reliablyengage with the inner link.

In another aspect of the invention, a multiple bicycle sprocket assemblycomprises a first sprocket and a second sprocket. The first sprocketincludes a first sprocket body, a plurality of first sprocket teeth, andat least one first shifting area. The first sprocket teeth are disposedalong a circumferential direction on a radially outer side of the firstsprocket body. The plurality of first sprocket teeth include at leastone first tooth and at least one second tooth. The at least one firsttooth has a first maximum axial width for engaging with an outer linkplate of the chain, and the at least one second tooth has a secondmaximum axial width for engaging with an inner link plate of the chain.The first maximum axial width is larger than the second maximum axialwidth. Meanwhile, the second sprocket includes a second sprocket bodyand a plurality of second sprocket teeth. The second sprocket teeth aredisposed along a circumferential direction on a radially outer side ofthe second sprocket body. All of second sprocket teeth have a thirdmaximum axial width for engaging with the inner link plate of the chain.The first maximum axial width is larger than the third maximum axialwidth.

According to the present invention, because at least one shifting areais provided to the sprocket, the shifting action is easier in a sprockethaving teeth that have different axial widths.

According to another aspect of the present invention, the chain can beheld in a stable manner on the first sprocket or the second sprocketduring the normal pedaling action.

Also other objects, features, aspects and advantages of the presentinvention will become apparent to those skilled in the art from thefollowing detailed description, which, taken in conjunction with theannexed drawings, discloses preferred embodiment of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a front view of a bicycle crank assembly according to thefirst embodiment of the present invention;

FIG. 2 is a front perspective view of the first sprocket;

FIG. 3 is a rear view of the first sprocket;

FIG. 4 is a partial rear perspective view of the first and secondsprockets;

FIG. 5 is a partial side view of the first sprocket, the secondsprocket, or the third sprocket as seen from the radially outer side;

FIG. 6 is a front perspective view of the second sprocket;

FIG. 7 is a front view of the bicycle crank assembly according to thesecond embodiment of the present invention; and

FIG. 8 is a surface view of the third sprocket.

DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the bicycle field fromthis disclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

In FIG. 1, a bicycle crank assembly (referred to as a crank assemblybelow) 10 according to the first embodiment of the present inventioncomprises a crank arm 12, and a first sprocket 14 and second sprocket 16which are bicycle sprockets according to an embodiment of the presentinvention. The first sprocket 14 and the second sprocket 15 are frontsprockets that can engage with a chain 2. The second sprocket 16 hasfewer teeth than the first sprocket 14. The chain 2 has an outer linkplate 2 a and an inner link plate 2 b.

Crank Arm

The crank arm 12 is integrally and rotatably linked to a crankshaft 19.The crank arm 12 has a sprocket attachment part 20, and an arm part 22provided either integrally to or separate from the sprocket attachmentpart 20.

The sprocket attachment part 20 has a plurality (e.g. four) of sprocketattachment arms 24 disposed at intervals in the circumferentialdirection. The circumferential intervals of the sprocket attachment arms24 may be equal intervals but may also be unequal intervals. In thefirst embodiment, the sprocket attachment arms 24 are disposed at equalintervals and are slanted upstream in advancing rotational direction Rof the crank arm 12 relative to the radial direction. The sprocketattachment arms 24 have first attachment parts 24 a for attaching thefirst sprocket 14. The first attachment parts 24 a are formed in thedistal ends of the sprocket attachment arms 24. The sprocket attachmentarms 24 have second attachment parts 24 b for attaching the secondsprocket 16. The second attachment parts 24 b are formed farther inwardin the radial direction than the first attachment parts 24 a. The firstattachment parts 24 a and the second attachment parts 24 b areconfigured from through-holes, for example, or screw holes or the likethrough which nothing else passes. In the first embodiment, the firstattachment parts 24 a are configured from through-holes, and the secondattachment parts 24 b are configured from screw holes through whichnothing else passes. The first sprocket 14 is fixed to the firstattachment parts 24 a by first fixing bolts 26. The second sprocket 16is fixed to the second attachment parts 24 b by second fixing bolts 28(see FIG. 4).

The arm part 22 is formed either integrally with or separate from thesprocket attachment part 20. In the first embodiment, the arm part 22 isconfigured integrally with the sprocket attachment part 20. The arm part22 has a pedal attachment part 22 a in which a pedal (not shown) can bemounted in the distal end, and a linking hole 22 b to which thecrankshaft 19 is integrally and rotatably linked in the proximal end.

First Sprocket

The first sprocket 14 has a rotational center axis X, and comprises afirst sprocket main body 30, a plurality (e.g. 30 to 60) of teeth 32disposed along the circumferential direction on the radially outer sideof the first sprocket main body 30, and a first shifting area 34, asshown in FIGS. 2 to 5. The first sprocket main body 30 is an example ofa sprocket main body. The first shifting area 34 is an example of ashifting area. The term “shifting area” in the present invention meanseither an area where the chain engages with the teeth of a largesprocket during an up shifting action from a small sprocket to a largesprocket, or an area where the chain separates from the teeth of thelarge sprocket during a down shifting action from the large sprocket tothe small sprocket. The first sprocket main body 30 and the teeth 32 aremade of metal and are formed integrally. The first sprocket main body 30has a plurality (e.g. four) of first fixed parts 30 a fixed to the firstattachment parts 24 a of the sprocket attachment arms 24 and disposed atintervals in the circumferential direction. In the first embodiment, thefirst fixing parts 30 a are configured from through-holes, and aredisposed in positions facing the plurality of first attachment parts 24a. The first sprocket 14 is fixed to the sprocket attachment arms 24 bythe first fixing bolts 26 and a nut member (not shown) threaded with thefirst fixing bolts 26.

There are thirty-six of the teeth 32 in the first embodiment, forexample. The teeth 32 include at least one first tooth 32 a having afirst maximum axial width W1 (see FIG. 5), and at least one second tooth32 b having a second maximum axial width W2. The first teeth 32 a areformed to be capable of engaging with an outer link plate 2 a of thechain 2. The second teeth 32 b are formed to be capable of engaging withan inner link plate 2 b of the chain 2. The first maximum axial width W1is greater than the second maximum axial width W2. The first maximumaxial width W1 of the first teeth 32 a is in a range of preferably 2.5mm or greater and 5.4 mm or less, and more preferably in a range of 3.0mm or greater and 4.5 mm or less. When the first maximum axial width W1of the first teeth 32 a is in such a range, the first teeth 32 a readilywith the outer link plate 2 a without engaging with the inner link plate2 b. The second maximum axial width W2 of the second teeth 320 ispreferably in a range of 1.5 mm or greater and 2.3 mm or less. When thesecond maximum axial width W2 of the second teeth 32 b is in such arange, the second teeth 32 b have the necessary rigidity and readilyengage with the inner link plate 2 b.

The first teeth 32 a are preferably formed into a + (plus) shape as seenfrom the radially outer side, as shown in FIGS. 2 to 5. The second teeth32 b are preferably formed into a − (minus) shape as seen from theradially outer side. The first teeth 32 a and the second teeth 32 b areformed tapering so as to gradually decrease in axial width toward theradially outer side. The first teeth 32 a and the second teeth 32 bthereby engage more readily with the outer link plate 2 a and the innerlink plate 2 b. Among the plurality of first teeth 32 a, first teeth 32a 1 and first teeth 32 a 2, which are shifting teeth 32 c describedhereinafter, are formed into T shapes as seen from the radially outerside in the first embodiment, as shown in FIG. 2. The first teeth 32 a 1are shifting teeth 32 c for down shifting wherein the chain 2 moves fromthe first sprocket 14 to the second sprocket 16, and the first teeth 32a 2 are shifting teeth 32 c for up shifting wherein the chain 2 movesfrom the second sprocket 16 to the first sprocket 14. The first teeth 32a 1 are an example of a second area of a shifting area, and the firstteeth 32 a 2 are an example of a first area of a shifting area. In thefirst embodiment, the first maximum axial width of the T-shaped firstteeth 32 a 1, 32 a 2 is less than the first maximum axial width W1 ofthe + shaped first teeth 32 a, and greater than the second maximum axialwidth W2 of the − shaped second teeth 32 b.

At least some of the first teeth 32 a and the second teeth 32 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 2.

The first shifting area 34 includes the first shifting teeth 32 c, whichare provided to at least one of the teeth 32. The first shifting teeth32 c are an example of shifting teeth. In the first embodiment, aplurality (e.g. four) of first shifting teeth 32 c is provided. Thefirst shifting teeth 32 c are provided between the linked first teeth 32a 1 and second teeth 32 b. The first shifting area 34 includes a firstprotuberance 36 a and a second protuberance 36 b, which are formed so asto be capable of supporting the chain 2. The first protuberance 36 a andthe second protuberance 36 b are an example of protuberances.Furthermore, the first shifting area 34 includes a concave part 38disposed farther diametrally inward than the roots of the teeth 32. Thebase portions 32 e correspond to the radially innermost portions of theteeth 32.

The first shifting teeth 32 c have first guide surfaces 32 d for guidingthe chain 2 in a first surface 14 a (see FIG. 2) side and a secondsurface 14 b (see FIG. 3) side of the first sprocket 14, as shown inFIGS. 2 and 3. The first guide surfaces 32 d are an example of a guidesurface. The first surface 14 a of the first sprocket 14 is the frontsurface disposed on the axially outer side farther from the bicycleframe when the crank assembly 10 is mounted to the bicycle. The secondsurface 14 b is the rear surface disposed on the axially inner sidenearer to the bicycle frame. The first guide surfaces 32 d are formed asbeing recessed so as to gradually decrease in thickness toward the sidesof the first shifting teeth 32 c.

The first protuberance 36 a is provided protruding in the second surface14 b of the first sprocket main body 30 in order to guide the chain 2 tothe teeth 32 of the first sprocket 14. The second protuberance 36 b isprovided protruding in the second surface 14 b of the first sprocketmain body 30 in order to guide the chain 2 to the first protuberance 36a. The first protuberance 36 a and the second protuberance 36 b are anexample of a first area of a shifting area. In the first embodiment, thefirst protuberance 36 a and the second protuberance 36 b are provided asa pair (a plurality) spaced at intervals in the circumferentialdirection. The first protuberance 36 a guides the chain to the secondteeth 32 b, which are shown by hatching in FIG. 3 and are upstream fromthe first protuberance 36 a in the advancing rotational direction R ofthe bicycle crank assembly 10 The first protuberance 36 a is providedprotruding in the second surface 14 b of the first sprocket main body 30in order to guide the chain 2 to the teeth 32 of the first sprocket 14.The second protuberance 36 b is provided protruding in the secondsurface 14 b of the first sprocket main body 30 in order to guide thechain 2 to the first protuberance 36 a. In the first embodiment, thefirst protuberance 36 a and the second protuberance 36 b are provided asa pair (a plurality) spaced at intervals in the circumferentialdirection. The first protuberance 36 a guides the chain to the secondteeth 32 b, which are shown by hatching in FIG. 3 and are upstream fromthe first protuberance 36 a in the advancing rotational direction R ofthe bicycle crank assembly 10.

The distance L1 between the first protuberance 36 a and the secondprotuberance 36 b is greater than the longitudinal length L2 of theouter link plate 2 a and/or the inner link plate 2 b of the chain 2, asshown in FIG. 1. The distance L1 between the first protuberance 36 a andthe second protuberance 36 b may also be either equal to thelongitudinal length L2 of the outer link plate 2 a and/or the inner linkplate 2 b of the chain 2, or less than the longitudinal length L2. Thefirst protuberance 36 a and the second protuberance 36 b are “swaged”securely to the first sprocket 14 by being plastically deformed. In thepresent embodiment, the first protuberance 36 a is larger in diameterthan the second protuberance 36 b.

The concave part 38 is formed in order to make it easier for the chain 2supported on the first protuberance 36 a to engage with the teeth of thefirst sprocket 14, as shown in FIGS. 3 and 4. Therefore, the concavepart 38 is disposed in proximity to the first protuberance 36 a andfarther diametrally (radially) inward than the base portion 32 e of theteeth 32. In the first embodiment, the concave part 38 is disposeddownstream from the first protuberance 36 a in the advancing rotationaldirection R, and is formed recessed into a substantially triangularshape which inclined upstream (clockwise in FIG. 3) from the diametrallyinner side to the outer side. The chain 2 is thereby readily supportedon the first protuberance 36 a.

Second Sprocket

The second sprocket 16 has a rotational center axis Y, and comprises asecond sprocket main body 40, and a plurality (e.g. 20 to 40) of teeth42 disposed along the circumferential direction on the radially outerside of the second sprocket main body 40, as shown in FIGS. 4 and 6. Thesecond sprocket main body 40 is an example of a sprocket main body. Asecond shifting area 44 is an example of a shifting area. The secondsprocket main body 40 and the teeth 42 are made of metal and are formedintegrally. The second sprocket main body 40 has a plurality (e.g. four)of second fixed parts 40 a fixed to the second attachment parts 24 b(see FIG. 1) of the sprocket attachment anus 24 and disposed atintervals in the circumferential direction. The second fixed parts 40 aare configured from through-holes, and are disposed in positions facingthe plurality of second attachment parts 24 b. The second sprocket 16 isfixed to the sprocket attachment arms 24 by the second fixing bolts 28(see FIG. 4) threaded with the second attachment parts 24 b.

The teeth 42 include at least one third tooth 42 a having a thirdmaximum axial width W3 (see FIG. 5), and at least one fourth tooth 42 bhaving a fourth maximum axial width W4. The third teeth 42 a are formedso as to be capable of engaging with the outer link plate 2 a of thechain 2. The fourth teeth 42 b are formed so as to be capable ofengaging with the inner link plate 2 b of the chain 2. The third maximumaxial width W3 is greater than the fourth maximum axial width W4. Thethird maximum axial width W3 of the third teeth 42 a is preferably in arange of 2.5 mm or greater and 5.4 mm or less, and more preferably in arange of 3.0 mm or greater and 4.5 mm or less. When the third maximumaxial width W3 of the third teeth 42 a is in such a range, the thirdteeth 42 a readily engage with the outer link plate 2 a without engagingwith the inner link plate 2 b. The fourth maximum axial width W4 of thefourth teeth 42 b is preferably in a range of 1.5 mm or greater and 2.3mm or less. When the fourth maximum axial width W4 of the fourth teeth42 b is in such a range, the fourth teeth 42 b have the necessaryrigidity and readily engage with the inner link plate 2 b.

The third teeth 42 a are formed into a + (plus) shape as seen from theradially outer side, as shown in FIGS. 4, 5 and 6. The fourth teeth 42 bare formed into a − (minus) shape as seen from the radially outer side.The third teeth 42 a and the fourth teeth 42 b are formed tapering so asto gradually decrease in axial width toward the radially outer side. Thethird teeth 42 a and the fourth teeth 42 b thereby engage more readilywith the outer link plate 2 a and the inner link plate 2 b.

At least some of the third teeth 42 a and the fourth teeth 42 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 6.

The second shifting area 44 includes the second shifting teeth 42 c,which are provided to at least one of the teeth 42. The second shiftingteeth 42 c are an example of shifting teeth. In the first embodiment, aplurality (e.g., two) of second shifting teeth 42 c is provided. Thesecond shifting teeth 42 c are provided at intervals in thecircumferential direction. The second shifting teeth 42 c have secondguide surfaces 42 d for guiding the chain 2 in a first surface 16 a (seeFIG. 6) side and a second surface 16 b (see FIG. 4) side of the secondsprocket 16, as shown in FIGS. 4 and 6. The second guide surfaces 42 dare an example of a guide surface. The first surface 16 a of the secondsprocket 16 is the front surface disposed on the axially outer sidefarther from the bicycle frame when the crank assembly 10 is mounted tothe bicycle, and the second surface 16 b is the rear surface disposed onthe axially inner side nearer to the bicycle frame. The second guidesurfaces 42 d are formed as being recessed so as to gradually decreasein thickness toward the sides of the second shifting teeth 42 c.

In the first embodiment, the second shifting area 44 may contain theprotuberances or concave part of the first shifting area 34. However,the second shifting area may also contain only the protuberances or onlythe concave part.

Shifting Action in Crank Assembly

In the bicycle crank assembly 10 having such a configuration. When theup shifting action from the second sprocket 16 to the first sprocket 14is performed by a front derailleur (not shown), the bicycle crankassembly 10 is rotated in the advancing rotational direction R. In thisstate, when the front derailleur moves from a position facing the secondsprocket 16 to a position facing the first sprocket 14, the chain 2separates from the teeth of the second sprocket 16. Having separatedfrom the second sprocket 16, the chain 2 is supported on the secondprotuberance 36 b and moved to the radially outer side, and is alsosupported on the first protuberance 36 a and guided to the teeth 32 ofthe first sprocket 14. At this time, the chain 2 is guided to the firstprotuberance 36 a by the concave part 38 of the first shifting area 34.Therefore, the chain 2 supported on the second protuberance 36 b isreliably supported on the first protuberance 36 a.

When a down shifting operation from the first sprocket 14 to the secondsprocket 16 is performed by the front derailleur (not shown), thebicycle crank assembly 10 is rotated in the advancing rotationaldirection R. In this state, when the front derailleur moves from aposition facing the first sprocket 14 to a position facing the secondsprocket 16, the chain 2 separates from the teeth of the first sprocket14. Having separated from the first sprocket 14, the chain 2 is guidedtoward the teeth 42 of the second sprocket 16 and engaged with the teeth42.

Second Embodiment

In the first embodiment, the bicycle crank assembly 10 has a firstsprocket 14 and a second sprocket 16, but the crank assembly 110 of thesecond embodiment further comprises a third sprocket 18 in addition, tothe first sprocket 14 and the second sprocket 16, as shown in FIG. 7.The third sprocket 18 has fewer teeth than the second sprocket 16. Thefirst sprocket 14 and the second sprocket 16 have the sameconfigurations as the first embodiment and are therefore denoted in FIG.7 by the same symbols and are not described.

Third Sprocket

The third sprocket 18 has a rotational center axis Z, and comprises athird sprocket main body 50, a plurality (e.g. 20 to 30) of teeth 52disposed along the circumferential direction on the radially outer sideof the third sprocket main body 50, and a third shifting area 54, asshown in FIG. 8. The third sprocket main body 50 is an example of asprocket main body. The third shifting area 54 is an example of ashifting area. The third sprocket main body 50 and the teeth 52 are madeof metal and are formed integrally. The third sprocket main body 50 hasa plurality (e.g. four) of third fixed parts 50 a fixed to the secondattachment parts 24 b (see FIG. 1) of the sprocket attachment arms 24and disposed at intervals in the circumferential direction. The thirdfixed parts 50 a are configured from through-holes, and are disposed inpositions facing the plurality of second attachment parts 24 b. Thethird sprocket 18, together with the second sprocket 16, is fixed to thesprocket attachment arms 24 by the second fixing bolts 28 (see FIG. 4)threaded with the second attachment parts 24 b.

The teeth 52 include at least one fifth tooth 52 a having a fifthmaximum axial width W5 (see FIG. 5), and at least one sixth tooth 52 bhaving a sixth maximum axial width W6. The fifth teeth 52 a are formedso as to be capable of engaging with the outer link plate 2 a of thechain 2. The sixth teeth 52 b are formed so as to be capable of engagingwith the inner link plate 2 b of the chain 2. The fifth maximum axialwidth W5 is greater than the sixth maximum axial width W6. The fifthmaximum axial width W5 of the fifth teeth 52 a is preferably in a rangeof 2.5 mm or greater and 5.4 mm or less, and more preferably in a rangeof 3.0 mm or greater and 4.5 mm or less. When the fifth maximum axialwidth W5 of the fifth teeth 52 a is in such a range, the fifth teeth 52a readily engage with the outer link plate 2 a without engaging with theinner link plate 2 b. The sixth maximum axial width W6 of the sixthteeth 52 b is preferably in a range of 1.5 mm or greater and 2.3 mm orless. When the sixth maximum axial width W6 of the sixth teeth 52 b isin such a range, the sixth teeth 52 b have the necessary rigidity andreadily engage with the inner link plate 2 b.

The fifth teeth 52 a are formed into a + (plus) shape as seen from theradially outer side, as shown in FIGS. 5 and 8. The sixth teeth 52 b areformed into a − (minus) shape as seen from the radially outer side. Thefifth teeth 52 a and the sixth teeth 52 b are formed tapering so as togradually decrease in axial width toward the radially outer side. Thefifth teeth 52 a and the sixth teeth 52 b thereby engage more readilywith the outer link plate 2 a and the inner link plate 2 b.

At least some of the fifth teeth 52 a and the sixth teeth 52 b aredisposed alternately in the circumferential direction, i.e. adjacent toeach other, and in the first embodiment all of these teeth are disposedin this manner as shown in FIG. 8.

The third shifting area 54 includes third shifting teeth 52 c, which areprovided to at least one of the teeth 52. In the second embodiment, aplurality (e.g., two) of third shifting teeth 52 c is provided. Thethird shifting teeth 52 c are provided at intervals in thecircumferential direction. The third shifting teeth 52 c have thirdguide surfaces 52 d for guiding the chain 2 in a first surface 18 a (seeFIG. 8) side and a second surface (not shown) side of the third sprocket18, as shown in FIG. 8. The third guide surfaces 52 d are an example ofa guide surface. The first surface 18 a of the third sprocket 18 is thefront surface disposed on the axially outer side farther from thebicycle frame when the crank assembly 10 is mounted to the bicycle, andthe second surface is the rear surface disposed on the axially innerside nearer to the bicycle frame. The third guide surfaces 52 d areformed as being recessed so as to gradually decrease in thickness towardthe sides of the third shifting teeth 52 c.

In the third embodiment, the third shifting area 54 may contain theprotuberances or concave part of the first shifting area 34. However,the third shifting area may also contain only the protuberances or onlythe concave part.

Other Embodiments

Embodiments of the present invention are described above, but thepresent invention is not limited to these embodiments; variousalterations can be made within a range that does not deviate from thescope of the invention. Particularly, the plurality of embodiments andmodifications disclosed in the specification and be arbitrarily combinedas necessary.

(a) The first and second embodiments give a front sprocket as an exampleof a bicycle sprocket, but the present invention is not limited as such.The present invention can also be applied to a rear sprocket.

(b) In the bicycle crank assembly of the first and second embodiments,first teeth and second teeth having different axial widths are providedto all of the sprockets, but the present invention is not limited assuch. Any sprocket (e.g. the second and/or third sprocket, small indiameter) may be configured from second teeth alone.

(c) In the first and second embodiments, the first teeth were formedinto + shapes or T shapes as seen from the radially outer side, but thepresent invention is not limited as such. These teeth may also be formedinto other shapes such as diamonds, trapezoids, triangles, and hexagons.

(d) In the first and second embodiments, the first shifting area 34 hasthe second protuberance 36 b, but a second protuberance 36 b need not beprovided.

(e) In the first and second embodiments, there are four sprocketattachment arms 24, but the number of sprocket attachment arms is notlimited to four.

(f) In the first and second embodiments, the sprocket main bodies andthe pluralities of teeth are formed integrally, but the presentinvention is not limited as such. The sprocket main bodies and thepluralities of teeth may be formed separately. The pluralities of teethmay be made of metal, for example, and the sprocket main bodies may bemade of a synthetic resin such as a carbon fiber reinforced resin or adifferent metal than the teeth, for example (a light metal such asaluminum, for example), to reduce weight.

(g) The shifting areas of the sprockets may include the − (minus) shapedsecond teeth 32 b, fourth teeth 42 b, and sixth teeth 52 b.

Also it will be understood that although the terms “first” and “second”may be used herein to describe various components these componentsshould not be limited by these terms. These terms are only used todistinguish one component from another. Thus, for example, a firstcomponent discussed above could be termed a second component andvice-a-versa without departing from the teachings of the presentinvention.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. A bicycle sprocket for engaging with a chain andhaving a rotational center axis, the bicycle sprocket being configuredto be included in a multiple sprocket assembly in a position adjacent toa small sprocket that is smaller than the bicycle sprocket, the bicyclesprocket comprising: a sprocket main body; a plurality of teeth disposedalong a circumferential direction on a radially outer side of thesprocket main body; and at least one shifting area including a firstarea where the chain engages with one of the plurality of teeth of thebicycle sprocket during a shifting action from the small sprocket to thebicycle sprocket and a second area where the chain separates from one ofthe plurality of teeth of the bicycle sprocket during a shifting actionfrom the bicycle sprocket to the small sprocket, the plurality of teethincluding at least one first tooth having a first maximum axial widthfor engaging with an outer link plate of the chain and at least onesecond tooth having a second maximum axial width for engaging with aninner link plate of the chain, the first maximum axial width beinglarger than the second maximum axial width.
 2. The bicycle sprocketaccording to claim 1, wherein the plurality of teeth include a pluralityof the first teeth.
 3. The bicycle sprocket according to claim 1,wherein the plurality of teeth include a plurality of the second teeth.4. The bicycle sprocket according to claim 1, wherein the plurality ofteeth include a plurality of the first teeth and a plurality of thesecond teeth.
 5. The bicycle sprocket according to claim 4, wherein atleast some of the plurality of first teeth and the plurality of secondteeth are disposed alternately in the circumferential direction.
 6. Thebicycle sprocket according to claim 1, wherein the first teeth and thesecond teeth are disposed adjacent to each other.
 7. The bicyclesprocket according to claim 1, wherein the first teeth are formed intoa + shape as seen from the radially outer side.
 8. The bicycle sprocketaccording to claim 1, wherein the first teeth are formed into a T shapeas seen from the radially outer side.
 9. The bicycle sprocket accordingto claim 1, wherein the first maximum axial width of the first teeth isin a range of 2.5 mm or greater and 5.4 mm or less.
 10. The bicyclesprocket according to claim 9, wherein the first maximum axial width ofthe first teeth is in a range of 3.0 mm or greater.
 11. The bicyclesprocket according to claim 1, wherein the second maximum axial width ofthe second teeth is in a range of 1.5 mm or greater and 2.3 mm or less.12. The bicycle sprocket according to claim 1, wherein the shifting areaincludes shifting teeth provided to at least one of any of the pluralityof teeth.
 13. The bicycle sprocket according to claim 12, wherein theshifting teeth have guide surfaces for guiding the chain.
 14. Thebicycle sprocket according to claim 13, wherein the shifting areaincludes at least one protuberance that is configured to support thechain, the at least one protuberance being provided on an opposite sideof the bicycle sprocket as the guide surfaces.
 15. The bicycle sprocketaccording to claim 1, wherein the shifting area includes at least oneprotuberance that is configured to support the chain.
 16. The bicyclesprocket according to claim 12, wherein the shifting area includes atleast one protuberance that is configured to support the chain.
 17. Thebicycle sprocket according to claim 16, wherein the shifting areaincludes a concave part that is disposed farther inward in a radialdirection than the roots of the plurality of teeth.
 18. The bicyclesprocket according to claim 15, wherein the at least one protuberanceincludes a first protuberance and a second protuberance that areconfigured to support the chain.
 19. The bicycle sprocket according toclaim 18, wherein a distance between the first protuberance and thesecond protuberance is longer than a longitudinal length of at least onethe outer and inner links of the chain.
 20. The bicycle sprocketaccording to claim 18, wherein a distance between the first protuberanceand the second protuberance is either equal to or shorter than alongitudinal length of at least one the outer and inner links of thechain.
 21. A multiple bicycle sprocket assembly comprising: a firstsprocket including a first sprocket body, a plurality of first sprocketteeth, and at least one first shifting area, the plurality of firstsprocket teeth being disposed along a circumferential direction on aradially outer side of the first sprocket body, the plurality of firstsprocket teeth including at least one first tooth having a first maximumaxial width for engaging with an outer link plate of the chain, and atleast one second tooth having a second maximum axial width for engagingwith an inner link plate of the chain, the first maximum axial widthbeing larger than the second maximum axial width; and a second sprocketincluding a second sprocket body and a plurality of second sprocketteeth, the second sprocket teeth being disposed along a circumferentialdirection on a radially outer side of the second sprocket body, all ofsecond sprocket teeth having a third maximum axial width for engagingwith the inner link plate of the chain, the first maximum axial widthbeing larger than the third maximum axial width.
 22. The bicyclesprocket according to claim 18, wherein the first protuberance and thesecond protuberance are at least partially disposed farther inward in aradial direction of the bicycle sprocket than roots of the plurality ofteeth.
 23. The bicycle sprocket according to claim 22, wherein the firstprotuberance and the second protuberance spaced apart from each other inthe circumferential direction.
 24. The bicycle sprocket according toclaim 23, wherein the shifting area includes a concave part that isdisposed between the first protuberance and the second protuberance. 25.The bicycle sprocket according to claim 23, wherein the firstprotuberance is larger than the second protuberance, and the firstprotuberance is disposed upstream from the second protuberance in anadvancing rotational direction of the bicycle sprocket.
 26. The bicyclesprocket according to claim 23, wherein one of the at least one secondtooth is disposed immediately upstream of the first protuberance in anadvancing rotational direction of the bicycle sprocket.
 27. The bicyclesprocket according to claim 1, wherein the shifting area includes aconcave part that is disposed farther inward in a radial direction thanroots of the plurality of teeth.
 28. The bicycle sprocket according toclaim 1, wherein the at least one shifting area includes a plurality ofthe shifting areas.
 29. The bicycle sprocket according to claim 28,wherein the at least one shifting area includes at least a pair of theshifting areas.
 30. The bicycle sprocket according to claim 1, whereinthe bicycle sprocket being a front sprocket.
 31. A bicycle sprocket forengaging with a chain and having a rotational center axis, the bicyclesprocket comprising: a sprocket main body; a plurality of teeth disposedalong a circumferential direction on a radially outer side of thesprocket main body; and at least one shifting area, the plurality ofteeth including at least one first tooth having a first maximum axialwidth for engaging with an outer link plate of the chain and at leastone second tooth having a second maximum axial width for engaging withan inner link plate of the chain, the first maximum axial width beinglarger than the second maximum axial width, the at least one first toothincluding a shifting tooth that is included in the at least one shiftingarea, the shifting tooth being formed into a T shape as seen from theradially outer side.
 32. A bicycle sprocket for engaging with a chainand having a rotational center axis, the bicycle sprocket comprising: asprocket main body; a plurality of teeth disposed along acircumferential direction on a radially outer side of the sprocket mainbody; and at least one shifting area, the plurality of teeth includingat least one first tooth having a first maximum axial width for engagingwith an outer link plate of the chain and at least one second toothhaving a second maximum axial width for engaging with an inner linkplate of the chain, the first maximum axial width being larger than thesecond maximum axial width, the first maximum axial width of the firstteeth being in equal to or larger than 2.5 mm and smaller than or equalto 5.4 mm.
 33. The bicycle sprocket according to claim 32, wherein thefirst maximum axial width of the first teeth is equal to or larger than3.0 mm and smaller than or equal to 4.5 mm.
 34. The bicycle sprocketaccording to claim 32, wherein the second maximum axial width of thesecond teeth is equal to or larger than 1.5 mm and smaller than or equalto 2.3 mm.
 35. The bicycle sprocket according to claim 23, wherein thefirst protuberance is disposed farther outward in the radial directionthan the second protuberance.